The present invention generally relates to a liquid crystal optical cross point switching device and, in particular, relates to such a device having exposed optical fiber cores disposed proximate a liquid crystal material.
One of the basic devices used in many communication systems is the so called "cross point switch". In principle, a cross point switch is a mechanism to simultaneously connect a pair of selected inputs to a pair of selected outputs. In the telephony field such a switch effects the connection of the pair of wires of each caller to the pair of wires of the party called to establish a telephone connection therebetween.
ln practice, the cross point switch is most frequently used as one element of a larger cross point switching matrix for cross connecting a substantial number of pairs of signals in a communication network. Present technology usually implements the cross point switching function by, for example, means of semiconductor circuitry. Nonetheless, the basic function of a cross point switching matrix remains fundamental for many communication systems.
One of the current trends in telecommunications is the use of optical fibers in place of the more conventional transmission media. One advantage of optical fibers is the larger available bandwidth handling ability thereof thus providing the capability to convey larger quantities of information for a substantial number of subscribers via a media of considerably smaller size. Further, since light waves are shorter than, for example, microwaves a considerable reduction in component size is possible. As a result, a reduction in material, manufacturing and packaging costs is derived. Further, optical fibers do not emit any electromagntic or radio frequency radiation of consequence and, hence, have negligible impact on the surrounding environment. As an additional advantage, optical fibers are much less sensitive to extraneous radio frequency emissions from surrounding devices and systems.
The liquid crystal optical switching devices that have been proposed to date, however, are quite expensive, not only because the specific elements of the switching device but also because of the cost of manufacturing such switching devices. Typical of currently proposed liquid crystal optical switching devices are those described in U.S. Pat. No. 4,201,442 issued to McMahon et al. on May 6, 1980, U.S. Pat. No. 4,278,327 issued to McMahon et al. on July 14, 1981 and U.S. Pat. No. 4,385,799 issued to Soref on May 31, 1983.
These devices require expensive trapezoidal prisms having four optically flat surfaces. Further, during the manufacture of such devices, the opposing base surfaces of pairs of trapezoidal prisms must be very accurately aligned, thereby adding a considerable expense to the manufacturing procedure of such devices. Many of the difficulties and expenses incurred with these proposed liquid crystal switching devices have been overcome by devices discussed and described in U.S. patent application Ser. No. 795,156, entitled LIQUlD CRYSTAL OPTICAL SWITCHING DEVICE and U.S. patent application Ser. No. 795,151, entitled LIQUID CRYSTAL OPTICAL SWITCHING DEVICE HAVING MINIMIZED INTERNAL LIGHT PATH, both filed on even date herewith. These latter two patent applications are incorporated herein by reference. Nevertheless, all of the above-referenced devices can generally be classified as "critical angle devices". That is, the inputs and outputs thereof must be arranged such that the light waves are conveyed into the device at, minimally, the critical angle with respect to the optical surface of the liquid crystal material. This, in itself, can be an expensive constraint in the manufacturing procedure of such liquid crystal optical switching devices.
Consequently, in order to more fully realize the advantages of an optical communications system there is a considerable need for a liquid crystal optical cross point switching device that does not depend on critical angle alignment.